The skin is the largest organ system in the body, providing a protective barrier between the internal and external environment. The skin is made up of connective tissue with a variety of cell types. With natural aging and ultraviolet light exposure there is a gradual thinning and decrease in structural integrity of the skin. Fibroblasts, the cells responsible for connective tissue production, exhibit enhanced proliferation and protein synthesis following heat stimulation. At the protein level, temperature elevation in the connective tissue of skin produces an effect on matrix proteins, such as collagen. Immediate collagen contraction is followed by deposition and remodeling. Therefore, energy delivery to the skin will promotes improved elasticity, dermal tightening and overall skin rejuvenation.
Light and heat exposure to the skin can also be used to treat acne and resolve the associated inflammatory response. Bacteria and sebum are two components of acne. Sebum, the oily or waxy secretion for lubrication and waterproofing the skin, accumulates during acne. Sebum also serves as a food source for bacteria thereby promoting bacterial growth and subsequent inflammation. During metabolism, bacteria produce porphyrins. Upon exposure to light of blue wavelengths, the porphryins become activated and cause bacterial death, ultimately helping clear the acne. Additionally, heat can have a dual function for acne. Heat can kill bacteria and help accelerate the resolution of the acne lesion. Together light and heat exposure to the skin can help treat and resolve acne lesions on the skin.
Subcutaneous fat is a widely distributed tissue layer beneath the skin that provides protection, thermoregulation, and an energy reserve. Subcutaneous fat is comprised of fat cells, which store triglycerides, and are separated into lobules by an organized by a network of fibrous septae. Composed from connective tissue, the fibrous septae occur parallel, perpendicular, or oblique to the skin surface.
Alterations in the subcutaneous tissue can result in skin surface topology changes, commonly called cellulite. Compared to normal tissue, cellulite may reflect differences in fat tissue biochemistry, or connective tissue structure. Disruptions in fat cell metabolism or fibrous septae orientation may result in focal herniation of fat into the skin producing surface distensions. Furthermore, skin damage or changes in elasticity are also associated with cellulite. Therefore the development of a novel, non-invasive method for fat reduction with simultaneous dermal tightening is needed.
Cellulite has a complex etiology and consequentially requires a multifaceted therapeutic approach. At the tissue level, temperature elevation improves capillary and lymphatic microcirculation. At the cellular level, temperature elevation influences fat cells and fibroblasts. The heating of fat cells induces metabolic alterations, membrane permeability for lipid release, apoptosis, and necrosis. Increased connective tissue production by heat-induced fibroblasts prohibit fat protrusion into the skin, and alleviate alterations in fibrous septae orientation. Therefore selective heating of skin and fat tissues will provide a customizable and effective remedy for subcutaneous tissue alterations.
In non-cellulite related applications such as skin rejuvenation and acne treatment, the skin is the primary target for energy delivery. Nonetheless, the ability to selectively heat both skin and fat may be advantageous. By either preheating subcutaneous fat prior to skin treatment, or by simultaneously delivering energy to the skin and subcutaneous fat, an effect can be achieved where deeper dermal layers are heated to higher temperatures as compared to the epidermis. Thus, an inverse temperature gradient in the skin can be achieved. Since nerve fibers are denser in the surface layers of the skin, a lesser amount of discomfort can be expected for treatments utilizing tissue-specific energy delivery.
Common technologies to deliver energy into the skin and fat include: laser and light emitting diode (LED) light, ultrasound and radio frequency (RF). RF heating is a preferred method of energy delivery when either a large volume of tissue is being treated and uniform energy absorption is sought, or greater penetration depths are required.
RF systems intended to treat skin and subcutaneous fat have been known in the art for a number of years. The vast majority of these systems use an RF energy source operating in the range of several hundreds of kilohertz (kHz) to several megahertz (MHz). These systems utilize either a small treatment electrode located on the handpiece coupled with a large return electrode attached to the patient, or a system of multiple small electrodes located on the handpiece.
Complications associated with monopolar RF systems utilizing a return electrode include the need for impedance matching (see U.S. Patent Application Publication No. 20070083247) and impedance sensing hardware (see U.S. Patent Application Publication No. 20070078502). Yet another complication occurring with all low frequency RF systems is the unwanted heating of the treatment electrode edges created by increased current density, or the so called “edge effect” phenomenon. To mitigate this effect, a complex cryogenic cooling system is frequently introduced (see U.S. Patent Application Publication No. 20020049483 and U.S. Pat. No. 6,413,255).
To selectively target a particular tissue layer some systems employ a multi-electrode energy delivery system that claims to influence the depth of energy delivery, although not the tissue type (see U.S. Patent Application Publication No. 20070088413). Other systems, (as described in U.S. Patent Publication No. 20100211060) purportedly selectively treat subcutaneous fat but not the skin. Yet other systems, purportedly target multiple tissue layers (see U.S. Patent Application Publication US 20100211059). However, such systems rely on the wide band RF energy source, making the overall apparatus complex. Also, it is also unclear if such a device is capable of selectively heating a fat layer that is several centimeters thick.
Thus, RF systems having the following improvements are needed:
(i) the capability to selectively heat skin and/or subcutaneous fat tissues, thereby providing new treatment options.
(ii) the capability to use a single frequency or a narrow band RF source, reducing the overall complexity and cost of the system.
(iii) uniform energy delivery by using an RF antenna based system operating near to, or in the microwave frequency range to eliminate the electrode edge effects that occur in the majority of the existing RF systems. Uniform energy delivery removes the requirement for a complex cryogenic cooling system for the treatment electrode and allows for accurate skin surface temperature measurements. Furthermore, uniform energy yields increased patient comfort, decreased procedural times and maintenance of therapeutic temperature levels; thereby providing improved clinical outcomes. As used herein, the term microwave is as defined in the seventh edition of IEEE 100, The Authoritative Dictionary of IEEE Standards Terms, “pertaining to the portion of the radio frequency spectrum above 1 GHz.”
(iv) elimination of the return electrode.